Discovered by Charles Darwin in 1834, Rhinoderma darwinii (better known as Darwin's frogs) have been declared extinct after a killer disease is thought to have wiped out entire populations across Chile and Argentina.

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According to scientists from the Zoological Society of London (ZSL) and Universidad Andrés Bello (UNAB), Chile, chytridiomycosis is the main reason for this amphibian extinction.

Although habitat disturbance is recognized as the main threat to the two existing species of Darwin's frogs (the northern Rhinoderma rufum endemic to Chile, and the southern Rhinoderma darwinii from Chile and Argentina), researchers believe this cannot account for the plummeting population and disappearance of the population.

Conservation scientists found evidence of amphibian chytridiomycosis causing mortality in wild Darwin's frogs and linked this with both the population decline of the southern Darwin's frog, including from undisturbed ecosystems and the presumable extinction of the Northern Darwin's frog.

Chytridiomycosis causes morphological changes in amphibians including reddening of ventral skin and convulsions with extension of hind limbs. The disease can also cause lethargy and failure to seek shelter.

Professor Andrew Cunningham, from ZSL's Institute of Zoology says: "Only a few examples of the 'extinction by infection' phenomenon exist. Although not entirely conclusive, the possibility of chytridiomycosis being associated with the extinction of the northern Darwin's frog gains further support with this study."

Hundreds of specimens of Darwin's frogs and other amphibians from similar habitats collected between 1835 and 1989 were tested in order to find DNA pieces of Batrachochytrium dendrobatidis (Bd), a fungus that causes the disease chytridiomycosis. In addition, 26 populations of Darwin’s frogs were surveyed in Chile and Argentina between 2008 and 2012 for the presence of Bd.

Research leader Dr. Claudio Soto-Azat, from UNAB and former ZSL PhD student said: "Amphibians have inhabited the earth for 365 million years, far longer than mammals. We may have already lost one species, the Northern Darwin's frog, but we cannot risk losing the other one. There is still time to protect this incredible species".

Amphibians provide an important ecosystem service by maintaining balance in the environment. Without them insect plagues and their subsequent effect on agriculture and public health would be more frequent. ZSL scientists are working to further understand the reasons behind the extinction of Darwin's frogs, and ensure the long-term survival of the species.